Orientation-controlled Si thin films on insulating substrates by Al-induced crystallization combined with interfacial-oxide layer modulation

Abstract

Orientation-controlled Si films on transparent insulating substrates are strongly desired to achieve high-efficiency thin-film solar cells. We have developed the interfacial-oxide layer modulated Al-induced low temperature (<450 °C) crystallization technique, which enables dominantly (001) or (111)-oriented Si films with large grains (20–100 μm). These results are qualitatively explained on the basis of a model considering the phase transition of the interfacial Al oxide layers. This process provides the orientation-controlled Si templates on insulating substrates, which enables successive high quality epitaxial growth necessary for advanced Si thin-film solar cells.

Highly (111)-oriented Ge thin films on insulators formed by Al-induced crystallization

“…This behavior is also the same as the AIC-Si. 13,14 The reason for this result can be explained as follows. The Ge nuclei occur on the SiO 2 substrate because the thicknesses of Ge and Al layers are thin (50 nm).…”

“…The lower T a and longer t air required the longer annealing times for the completion of the AIC: (a) 10 h, (b) 30 h, (c) 100 h, (d) 10 h, (e) 30 h, (f) 100 h, (g) 30 h, (h) 100 h, and (i) 400 h. The AIC of a-Si had the same trend. 13,14 This trend can be explained as follows: The low T a decreases the reaction rates by the Arrhenius law 20 ; and the longer t air thickens the AlO x intermediate layer thickness, and thereby reducing the interdiffusion rate of Al and Ge atoms. 12,13 These orientation mappings clearly indicate that the orientation of the AIC-Ge depends on both T a and t air : (111) orientation becomes dominant with decreasing T a and increasing t air .…”

“…[10][11][12][13][14][15] This AIC technique enables us to form large-grain (diameters: 10-100 lm) polycrystalline Si films at relativity low temperatures (420-550 C) through the exchange between the Al and Si layers during annealing. [10][11][12][13][14][15] Moreover, we controlled the orientations of the Al-induced-crystallized Si (AIC-Si) films to either (100) or (111) plane by modulating the annealing temperatures, the thickness of Al and Si layers, and the thickness of Al native oxide (AlO x ) interlayers between Si and Al layers. [13][14][15] CVD of Si layers onto the AIC-Si thin-film is a promising approach to fabricate the low-defect Si layers on glass substrates.…”

“…[10][11][12][13][14][15] Moreover, we controlled the orientations of the Al-induced-crystallized Si (AIC-Si) films to either (100) or (111) plane by modulating the annealing temperatures, the thickness of Al and Si layers, and the thickness of Al native oxide (AlO x ) interlayers between Si and Al layers. [13][14][15] CVD of Si layers onto the AIC-Si thin-film is a promising approach to fabricate the low-defect Si layers on glass substrates. 16,17 Based on these findings on AIC-Si, [13][14][15] we recently investigated the AIC of amorphous Ge (a-Ge) on quartz glass substrates.…”

“…[13][14][15] CVD of Si layers onto the AIC-Si thin-film is a promising approach to fabricate the low-defect Si layers on glass substrates. 16,17 Based on these findings on AIC-Si, [13][14][15] we recently investigated the AIC of amorphous Ge (a-Ge) on quartz glass substrates. As a result, we achieved preferentially (111)-oriented ($68%) poly-crystalline Ge (poly-Ge) by thinning both Ge and Al layers (50-nm thickness).…”